<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box {
      width: 400px;
      height: 300px;
      border: 1px solid rgba(6, 39, 69, 0.6);

      position: relative;
    }

    .box::before {
      content: "";
      width: 10px;
      height: 10px;
      display: block;
      border-top: 1px solid #02a6b5;
      border-left: 1px solid #02a6b5;

    }

    .box::after {
      content: "";
      width: 10px;
      height: 10px;
      display: block;
      border-top: 1px solid #02a6b5;
      border-right: 1px solid #02a6b5;

      position: absolute;
      right: 0px;
      top: 0px;


    }
  </style>
</head>

<body>
  <div class="box"></div>

</body>

</html>